The impetus for this Program Project on genetic approaches to cardiac development arises from the indispensable importance of cardiac organogenesis for survival even during embryonic life, and from the conviction that fundamental knowledge gained from studies of cardiac development in model organisms is ultimately essential to understanding the failure of normal cardiac morphogenesis, manifested as congenital heart disease. Understanding the mechanisms that control the early events in heart development will also have relevance to adult heart disease, which is often associated with reactivation of the fetal program for cardiac gene expression. In fact, understanding how cardiogenic cells become specified will have a great impact in repairing damaged heart by stem cell and or somatic cell therapy. Systematic studies of the cis-acting sequences that control cardiac-restricted genes, the trans-acting factors binding these regions, circuits governing the factors' expression or function, and other circuits affecting morphogenesis itself have, in these five years, culminated in gratifying new insights and opportunities within the field, in large part through the efforts of these PPG investigators. Transcriptional Regulation of Embryonic Cardiogenesis: Nkx-2.5 gene regulation via BAC transgenics and interacting proteins, focused on SRF, CRP 1/2/3 lim only factors, GATA-4 and dHAND and their knockouts, including an emphasis on combinatorial transcription factor complexes with SRF (Schwartz) Genes That Regulate Heart Development: Myocardin, interacting proteins, Myocardin relatives and knockouts, with an emphasis on the association with SRF and other Myocardin accessory factors (Olson) Adult Cardiac Myogenesis by Heart-derived Progenitor Cells. Adult cardiac stem cells depend on Bmpr1a-dependent differentiation of adult, with emphasis on the signaling and transcriptional mechanisms for induction of Nkx2.5. (Schneider); Supporting cores include an Informatics Microarray. ES Cells and Microinjection, Embryology, and Adminstration A unifying theme of this PPG renewal is that specification of cardiac lineages and expression of cardiac restricted genes requires combinatorial interactions between core transcription factors found to be enriched during the emergence of cardiac progenitor cells and in adult cardiac stem cells. This theme resonates well with elucidating the role for the complex and modular regulatory enhancers/repressors that direct expression of these cardiogenic transcription factors. In this PPG, we are still tightly focused on the use of mouse genetics. In addition to more conventional approaches (gain-of-function mutations in transgenic mice and loss-of-function mutations through homologous recombination), we have already made heavy use of promoter mapping in transgenic mice with BACs, investigated cardiaclethal transgenes in F0 embryos, implemented cardiac-restricted knockout mutations by directing Cre recombinase to the developing heart. The implementation of enhanced informatics to identify direct and indirect genetic targets responsive to alterations in the cardiogenic differentiation programs will be a great addition to our PPG. To a greater extent than before, these approaches allow us not only to investigate the mechanisms for cardiac myocyte differentiation and morphogenesis but also for novel insights for cardiac repair via adult cardiac stem cells.